Tibial muscular dystrophy. Late adult-onset distal myopathy in 66 Finnish patients.

Objective: To clarify the classification of two previously reported groups of patients with anterior tibial distal dystrophy, to find additional patients with the disease, and to describe the clinical features of this disease.

Design: National survey of the records of patients with neuromuscular diseases in Finland. Findings of selected patients were compared with those of previously reported cases.

Patients: Thirty-six previously described patients and 30 additional patients from the current survey, with 41 symptomatic patients and 25 subjectively asymptomatic affected relatives.

Results: There were 66 patients with late adult-onset tibial muscular dystrophy. Symptoms appear after the age of 35 years with reduced ankle dorsiflexion, and progress is slow without marked disability. Facial muscles, upper extremities, and proximal muscles are usually spared. Muscle biopsy results reveal nonspecific dystrophic changes in clinically affected muscles, and frequently severe adipose replacement in the anterior tibial muscles occurs. Asymptomatic muscles have mild myopathic changes only. Vacuolar degeneration is detected in a minority of patients. Electromyography shows profound myopathic changes in the anterior tibial muscle, but extensor brevis muscles are well preserved. Computed tomography or magnetic resonance imaging of muscles discloses marked involvement of tibial extensor muscles and focal patches of fatty degeneration in various asymptomatic muscles. Pedigree data suggest autosomal dominant inheritance.

Conclusions: Tibial muscular dystrophy might represent a new form of distal myopathy and it is rather common, at least in Finland.